In recent years, with the diversification of vehicle control such as driving assist control and autonomous driving control, the scale of application programs such as vehicle control and diagnosis installed in electronic control units (ECUs) of the vehicle is increasing. In addition, with the version upgrade to improve functions, the opportunity to rewrite (reprogram) application programs of the ECUs is also increasing. On the other hand, with the development of communication network technologies, technologies related to connected cars are also developing. Under such circumstances, update programs for ECUs have been transmitted through OTA (Over The Air) to rewrite programs of the ECUs in vehicles.